GB-A-2139898 describes a deformable polymeric composition which can absorb liquid and thereby expand or contract in one direction without similar expansion or contraction in another direction. In particular, GB-A-2139898 describes an insert plug for dental cavities, which can absorb liquid and thereby expand radially without expanding axially. The material is such that it does not expand isotropically or uniformly (as a percentage of its initial dimensions) in every direction but, instead, has different expansion properties in different directions. Since the composition does not expand axially, it does not load the final cosmetic surface applied to the outer surface of the cavity and, since it expands laterally, it is possible to achieve a good fit by selection out of a relatively small number of inserts, relative to traditional rubber inserts. Other compositions described in GB-A-2139898 are surgical inserts, such as breast implants and nerve approximation sheaths.
GB-A-2340430 describes a dental insert plug of a prestressed hydrophilic material, the material prestressed by the application of pressure in the temperature range of 100 to 160° C.
Although insert plugs such as those described above achieve a relatively good fit, gaps may still remain between the walls of the cavity and the insert plug. Consequently, a sealant must be used to seal these gaps. There still remains the need for compositions whose shape change and/or expansion properties can be accurately controlled and predetermined.